Crosslinking can be accomplished in a variety of ways, including chemically or by energy exposure, which can induce a conformational or internal chemical change in a material. Incorporation of photosensitive groups to a material allows on-demand polymerization with the application of ultraviolet (UV) light. Photosensitive polymers often are used in the fields of printing, inks, coatings, drug delivery, and tissue engineering. The photosensitive groups in the main or pendant chains of a polymer can polymerize or cleave after irradiation with UV light, depending on whether the groups are of a negative or positive type. This photosensitive capability can enhance the precision and control of the crosslinking of the material, whereas other types of polymerization cannot be controlled on demand. Conversely, polymers with o-nitrobenzyl moieties can efficiently transfer electrons upon UV irradiation, which results in the cleavage of the polymeric chains. However, none of these photosensitive materials is reversible, which forces a user to choose between the benefits of photopolymerization or photocleavage, exclusively.
One of the most appealing ways to control the application of materials to a specific site is by applying a material in a pre-state that can flow and integrate into irregular surfaces, increasing the surface area for interaction, and then crosslinking the material to fix it into place. Materials are desired that can reversibly crosslink on command.
There are several biocompatible adhesives that are commercially available. The commercially available adhesives, however, typically are difficult to remove. Healing and adhesion often create a powerful bond between the patient's tissues and the adhesive material, thereby preventing the removal of the adhesive material without disrupting the wound and potentially causing further injury. Therefore, first responders who need to control a wound immediately must decide whether applying the currently available adhesive materials is optimal for long term treatment.
It would be advantageous to have an adhesive or material that can stabilize a wound or serve another purpose, such as drug delivery, and prevent further injury while allowing health care providers to later selectively remove the material, for example, to permit further treatment, or to later activate the material to control drug release.